Normally, it takes wins in five full matches to reach a grand slam semi-final. Novak Djokovic has made it that far at the US Open by playing only two, because three opponents pulled out of the tournament with injuries.
Djokovic, the No.1 seed and defending champion, once again needed to put in very little work, advancing to the final four at Flushing Meadows for the 10th consecutive year when Jo-Wilfried Tsonga stopped because of an injured left knee on Tuesday night.
The first two sets of their quarter-final went Djokovic's way 6-3 6-2.
At the ensuing change over, Tsonga was visited by a trainer and had his left leg taped below the knee.
They played one point to begin the third set: Tsonga double-faulted, then retired from the match.
This came after Djokovic's second-round opponent, Jiri Vesely, withdrew from the tournament with a sore left forearm. And then the man Djokovic was supposed to play in the third round, Mikhail Youzhny, quit after six games and only 31 minutes with a strained left hamstring.
"Of course, this grand slam is very unique for me: I never experienced something like this - to have three retirements on the road to the semi-finals," Djokovic said.
Tsonga said when the pain came "I knew it was over for me straightaway."
"It's already tough to play against one of the best tennis players," Tsonga said, "but when I don't have my knee, I have no chance to come back from two sets to love."
On Friday, Djokovic will play No.10 Gael Monfils, who advanced earlier against No.24 Lucas Pouille, the man who eliminated Rafael Nadal in the fourth round.
Playing steadily, and with only a dose of the spectacular, Monfils reached his first major semi-final since 2008 by beating an error-prone Pouille 6-4 6-3 6-3 in an all-French quarter-final.
For all of his deep runs at Flushing Meadows, Djokovic has won only two of his 12 grand slam titles at the hard-court tournament, in 2011 and 2015. He's lost in four finals and three semi-finals over the past decade.
It's tough to know exactly how well he's playing at the moment, simply because no one has seen him on court all that much lately: less than six hours through five rounds.
After his streak of four consecutive major championships - the first time a man had done that in nearly 50 years - was capped by his initial French Open title, Djokovic was upset in the third round at Wimbledon.
He returned to action by winning the Toronto Masters, but since then, Djokovic lost in the first round of the Rio Olympics while dealing with a sore left wrist that he then cited in skipping the Cincinnati Masters.
Djokovic's right arm was massaged by a trainer in his first and fourth-round matches at the US Open, so getting all of these free passes hasn't been a bad thing.
"In this stage of the season, considering some physical issues I have had in the last month, month and a half, this was the scenario that I needed and I wished for. I got a lot of days off and recovered my body," Djokovic said.
"Right now, I'm feeling very close to the peak. That's the position where I want to be."
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